1. Field of the Invention
The present invention relates to an AF auxiliary light projector for a camera having an autofocus system.
2. Description of the Related Art
Some SLR cameras and camcorders which incorporate a passive autofocus system are provided with an AF auxiliary light projector which emits an auxiliary light beam with a predetermined contrast pattern (e.g., a pattern of stripes) toward the object in low-light or low contrast situations to aid the autofocus system. It is desirable for the AF auxiliary light coverage to range from a near distance range to a far distance range. However, it is difficult to give a sufficient amount of AF auxiliary light to the object at a far distance since the light amount decreases as the AF auxiliary light projector is farther from the object. In AF cameras in which a distance measuring zone can be freely set within a photographing range and in AF cameras in which focus information is obtained from each of different distance measuring zones within a photographing range, the light projection area of the AF auxiliary light is desirably large. To increase the light projection area of the AF auxiliary light, it is conventionally the case that a large contrast pattern chart for forming the aforementioned predetermined contrast pattern is used, or that a contrast-pattern projecting lens having a short focal length is used. However, a large contrast pattern chart has to be illuminated if used for forming the predetermined contrast pattern, which leads to an increase in size of the illuminating lens system. In the case where a contrast-pattern projecting lens having a short focal length is used, the projection scaling factor of the contrast pattern increases to thereby decrease the amount of the AF auxiliary light projected onto the object, which inevitably decreases the performance of the AF system for far distance objects.
The present invention has been devised in view of the problems noted above, and accordingly, the present invention provides a compact AF auxiliary light projector wherein the AF auxiliary light coverage ranges from a near distance range to a far distance range.
For example, an AF auxiliary light projector for an AF camera is provided, including a focus detection optical system having a first optical axis, and an AF auxiliary light projecting optical system having a second optical axis which intersects the first optical axis, the AF auxiliary light projecting optical system projecting an image having a predetermined contrast pattern onto a photographic object. The AF auxiliary light projecting optical system includes a projector lens, a contrast pattern chart for forming the predetermined contrast pattern, an illumination lens, and an illumination light source, in that order from an intersection between the first optical axis and the second optical axis. The illumination lens is formed having an asymmetrical optical power so that an optical power of a far distance portion of the illumination lens for a far distance region in a projection region of the contrast pattern chart is greater than an optical power of a near distance portion of the illumination lens for a near distance region in the projection region of the contrast pattern chart.
It is desirable for the illumination lens to be formed so as to satisfy the following condition:
hN/hF greater than 1.2; wherein xe2x80x9chNxe2x80x9d designates a height of a first light ray from the second optical axis which is passed through the contrast pattern chart upon being emitted from the illumination light source to be incident on the near distance portion of the illumination lens at a first angle defined between the second optical axis and the first light ray; and xe2x80x9chFxe2x80x9d designates a height of a second light ray from the second optical axis which is passed through the contrast pattern chart when the second light ray is emitted from the illumination light source to be incident on the far distance portion of the illumination lens at a second angle defined between the second optical axis and the second light ray, the absolute value of the second angle being the same as the absolute value of the first angle, and the angular orientation of the second angle being opposite to the angular orientation of the first angle.
It is desirable for an angle of inclination of the second optical axis relative to the first optical axis and an angle of inclination of the contrast pattern chart relative to the second optical axis be determined so that a conjugate image of the contrast pattern chart is formed on a plane extending in a direction substantially parallel to the first optical axis.
It is desirable for the focus detection optical system to be provided as a multi-zone focus detection optical system for obtaining focus information from each of a plurality of different detection zones.
The illumination light source can be provided as a plurality of illumination light sources, and the illumination lens can be formed as a combination of a plurality of condenser lenses which condense light bundles emitted from the plurality of illumination light sources, respectively.
In another embodiment, an AF auxiliary light projector for an AF camera is provided, including a focus detection optical system having a first optical axis, and an AF auxiliary light projecting optical system having a second optical axis which intersects the first optical axis, the AF auxiliary light projecting optical system projecting an image having a predetermined contrast pattern onto a photographic object. The AF auxiliary light projecting optical system includes a projector lens, a contrast pattern chart for forming the predetermined contrast pattern, an illumination lens, and an illumination light source, in that order from an intersection between the first optical axis and the second optical axis. At least one of front and rear surfaces of the illumination lens is decentered from the second optical axis so that a luminous intensity of a far distance region in a projection region of the contrast pattern chart becomes greater than a luminous intensity of a near distance region in the projection region of the contrast pattern chart.
It is desirable for an angle of inclination of the second optical axis relative to the first optical axis and an angle of inclination of the contrast pattern chart relative to the second optical axis be determined so that a conjugate image of the contrast pattern chart is formed on a plane extending in a direction substantially parallel to the first optical axis.
It is desirable for the focus detection optical system to be provided as a multi-zone focus detection optical system for obtaining focus information from each of a plurality of different detection zones.
The illumination light source can be provided as a plurality of illumination light sources, and the illumination lens can be formed as a combination of a plurality of condenser lenses which condense light bundles emitted from the plurality of illumination light sources, respectively.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2001-172284 (filed on Jun. 7, 2001) which is expressly incorporated herein by reference in its entirety.